Well I read the water article Mr E but there are still some things I don't get....all those ferts etc are supposed to already have ph buffers in them. Why aren't they working for you??!! I did notice however that when I mix a new batch of ferts the ph is usually low and I bring it up with baking soda before I do a res change so perhaps I've just plain been way ahead of you the whole time.....the last few times I have done res changes I have not had to raise my ph first and now thinking about it I realize that the ph is not staying as stable at first as it was but settles down pretty well after I adjust it with ph down for the first time. (Always goes up.... never down so ha)